The present invention is applied to a substrate which is provided with a substrate main body mainly made of silicon and an oxide film for a base formed on the substrate main body. In such a substrate, due to a difference in thermal shrinkage characteristic between the oxide film and another film formed on the oxide film, a stress difference is generated between the oxide film and the other film, for example, after an annealing process, with the result that cracks might generate on the oxide film or the other film, or both of the oxide film and the other film due to the stress difference.
With respect to this problem, in a conventional substrate, the oxide film used for the base is formed by a thermal SiO2 film which is made by thermally oxidizing silicon in the substrate main body. The resulting problem with such a conventional substrate is that a stress difference, generated between the oxidized SiO2 film and another film formed thereon upon thermal shrinkage, tends to become greater. Moreover, in an attempt to make the film thickness of the oxide film used for the base thicker, there is degradation in the efficiency of the thermally oxidizing process due to the increased film thickness, and it takes a long time to form the oxide film.